Design for Maintainability (DFM) 

Introduction

The pressures of a global market continue to force companies to consider all aspects of product performance in an effort to remain competitive. An important aspect of product performance is maintainability. This START Sheet provides some insights into designing a product for maintainability.

Many durable products require maintenance throughout their useful life. Thoughtful consideration of a products maintenance features early in the design process can reduce or eliminate maintenance costs, reduce downtime, and improve safety.

What is design for maintainability? First, design is the transformation of an idea into a product, process, or service that meets both the designers requirements and end users needs. Second, maintainability is the degree to which the design can be maintained or repaired easily economically and efficiently. We can now define design for maintainability as a design strategy, involving both the designer and end user, with the following objectives.

Identify and prioritize maintenance requirements. Increase product availability and decrease maintenance time.

Increase customer satisfaction.

Decrease logistics burden and Life Cycle Costs.

The effectiveness of a design for maintainability strategy can be measured using maintenance metrics and industry benchmarks.

This START Sheet covers design for maintainability principles, benefits, and measurement.

Principles of Design for Maintainability

The notion that a products maintainability should be given strong consideration in the initial product development stage is driven by the fact that maintenance and the associated costs are accrued over the entire life of the product. Because maintenance costs can be a significant factor in a products overall cost, it is essential that maintenance be considered early in the design when flexibility is high and design change costs are low. As shown in Figure 1, design flexibility is greatest in the conceptual stage of the product and design change costs are low. As the product nears production, design flexibility decreases and design

change costs rise. Some companies report that changes made in production cost 100 to 1000 times as much as those made in the early concept stage. 

Figure 1. Product Phase vs. Product Costs/Flexibility (Click to Zoom)

Addressing maintainability during design reduces the end users maintenance costs over the products life. It may, however, increase the costs to manufacture. For example, it is cheaper and faster to spot weld panels together rather than use many fasteners. But welded panels would make it very difficult and expensive to make repairs in the field. By increasing product availability, a manufacturer can increase market share and enjoy a higher production run and higher profits over the life of the product. Customers get a product that is economical to operate and is available when needed.

Design for Maintainability (DFM) is a closed loop process using the following principles:

1. Use a team approach with DFM as a goal. A companys product development team should include individuals involved with design, manufacturing, product maintenance, and customer support.

2. Gather maintenance data and develop into information. Maintenance data can be gathered from the companys service people, field data collection system, customer surveys, and warranty information. The data is then developed into information that supports decisions.

3. Develop/identify maintenance concepts using information. Some customers will dictate the maintenance concept they will use. In other cases, the manufacturer must develop the maintenance concept. The product development team can generate product maintenance concepts

based on the information from Step 2. The selected maintenance concept is an important design constraint.

4. Design product using selected maintenance concepts. The design process begins using a systems approach and a variety of design tools, design rules, and approaches. At this stage, flexibility is great and design change costs are low.

5. Design, analyze, test, and improve the product. Based on the results of analysis and test (a prototype of portions of the product or even the entire product may be built), the design evolves. Maintenance concepts are reviewed and possibly revised. Flexibility is decreasing and design change costs are rising.

6. Manufacture the product and release to market. Engineering finalizes the design and releases the product to manufacturing. At this point, flexibility to modify the product maintenance features is low and the change costs are high.

7. Collect field maintenance data and develop information. Collect product field data in the form of customer feedback, warranty information, surveys, and service work. The information derived from this data can be used to evaluate the performance of the product in the field (Step 8) and in designing new products (Step 9).

8. Make field improvements as required by safety, economics, and other factors. Initial field performance may be lower than anticipated and additional changes to the design, procedures, or maintenance concept must be considered. At this point, modifying the product is very difficult and expensive. Only those changes dictated by customer acceptance or safety, or that are economically attractive will be made.

9. DFM process repeats with next generation product. Based on information generated from the field data, the design for maintainability process is repeated for the next generation product. Design rules may be revised, new tools developed, and design approaches validated or revised.

Design for Maintainability Features and Benefits

The objective of the design for maintainability is to provide benefits (value) to both the manufacturer and the end user. As quality and price differences among products diminish, manufacturers must find other incentives to convince customers to purchase their products. One such incentive is a high level of maintainability.

Durable products have long life cycles and many require both scheduled and

unscheduled maintenance throughout their lives. Companies with a disciplined DFM program can design maintainability into their products and use this attribute as a discriminator, making their product more attractive to customers.

Table 1 lists typical design for maintainability features used in the product development stage and the benefits these features provide to the designer and the customer. Note that Table 1 lists DFM features and benefits found in many electromechanical products. DFM can also be used for software, service operations, and processes.

While the DFM features and benefits in Table 1 might seem obvious, without the design for maintainability process, many of the features that make a product maintainable might not be realized during the product development stage.

Measuring the Benefits of Design for Maintainability

Table 2 lists several metrics that can be used in measuring design for maintainability benefits. This list is not inclusive and may vary depending on the product and/or industry. As Table 2 shows, maintenance metrics can be generated using a number of data sources.

Table 3 lists several industry maintenance cost benchmarks collected by the Plant Maintenance Resource Center (http://plantmaintenance.com/benchmarking.shtml). A company can compare its own maintenance metrics with benchmarks like these to determine the level of maintenance competency.

Table 1. Design for Maintainability Features/Benefits MatrixDesign for Maintainability Benefits Design for Maintainability Features

Easy access to serviceable items Maintenance time and costs reduced

Product availability increases

Technician fatigue/injury reduced

No or minimal adjustment Maintenance time and costs

reduced

Product availability increases

Maintenance training curve reduced

Components/modules quick and easy to Technician fatigue/injury reduced

replace

Product availability increases

Problem identification improvesMistake proofing, part/module installs one way only

Probability of damage to the part or product reduced

Reliability improves

Maintenance training curve reduced

Self-diagnostics or built in test or indicators to find problems quickly

Maintenance time and costs reduced

Product availability increases

Customer satisfaction improvesNo or few special hand tools Maintenance investment reduced

Customer satisfaction improves

Tool crib inventory reducedStandard fasteners and components No. of spare parts in inventory

reduced

Product cost reduced

Maintenance time and costs reduced

Reduce number of components in final assembly

Product cost reduced

Reliability improves

Spare parts inventory reduced

Table 2. Design for Maintainability MetricsMaintenance Metrics

Design Attributes Field Costs Field Performance Accessibility

Testability

Standardization

Repair Costs

Total Costs

Maintenance Payroll

Maintenance Mgt.

Maintenance Work Orders/Year

Downtime

Total Maintenance Hours

Human-factors

Times to Repair

Costs

Training Costs

No. of Maintenance Personnel

Induced Failures

Table 3. Industry Maintenance Benchmark Information  Maintenance Costs % of Total

CostsMaintenance Costs % of Plant

Replacement ValueOil and Gas Extraction

Best 27.50% 2.91%Worst 49.41% 21.76%

  Manufacturing: Metal ProductsBest 2.68% 0.83%

Worst 50.00% 11.76%  Utilities: Electricity Generation

Best 8.98% 1.34%Worst 66.89% 12.50%

  Forestry and LoggingBest 12.50% 100.00%

Worst 12.50% 250.00%  Mining: Metal Ore

Best 25.00% 6.99%Worst 40.41% 20.00%

  Manufacturing: FoodBest 2.50% 0.20%

Worst 46.15% 81.25%  Manufacturing: Wood & Paper Products

Best 0.98% 1.64%Worst 33.82% 8.54%

  Chemical & Associated ProductsBest 0.00% 0.00%

Worst 53.26% 150.00%  Manufacturing: Machinery & Equipment

Best 2.00% 0.79%Worst 2.00% 0.79%

Note:1. "Maintenance Costs % of Total Costs" is the annual maintenance cost as a

percentage of total annual plant costs.2. "Maintenance Costs % of Plant Replacement Value" is the maintenance

cost as a percentage of plant asset replacement value at a given time.

Reprinted with permission from the Plant Maintenance Resource Center.http://plant-maintenance.com/benchmarking.shtml